We observed comet C/1995 O1 (Hale-Bopp) at 4.6–2.9 AU pre-perihelion and 2.8–12.8 AU
post-perihelion with optical long-slit spectroscopy. Emission
bands of CN, C3, C2 and NH2 have been covered. Emission
of C3 was detected up to 7.0 AU, and CN could be followed up to
9.8 AU post-perihelion. Spatial column density profiles of the
radicals have been used to derive effective parent Haser scale
lengths for heliocentric distances beyond 3 AU. Production rates
were derived based on these Haser scale lengths. The observations
of CN are in agreement with HCN as the major parent molecule of
this radical at large distances from the Sun (i.e. beyond ~3
AU). We compare the measured CN production rate to sublimation
rates of HCN from a simple nucleus sublimation model. The
variation of CN production rates with changing heliocentric
distance gives no indication for sublimation from the interior and
is consistent with very little thermal lag of the nucleus.

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